The present invention relates to a technique of applying a femto slider to a magnetic disk drive with a magnetic disk mounted thereon, the magnetic disk including a track of a low linear velocity due to a low rotational velocity or a small radius up to an innermost radius track.
A slider used in a magnetic disk drive shows a continuous downsizing tendency because of a great advantage resulting from the reduction of size. As to an external size of the slider, a standard is defined by IDEMA (International Disk Drive Equipment and Materials Association). According to the standard, the size of a “mini slider” of 4.06 mm×3.2 mm×0.86 mm is designated 100% size and is used as a reference value; likewise, in order of size, there are defined “micro slider” (70%), “nano slider” (50%), “pico slider” (30%), and “femto slider” (20%).
The femto slider is the smallest in size among the sliders available at present. Its external size is 0.85 mm×0.7 mm×0.23 mm. Reducing the external size of a slider is advantageous in point of cost because the number of sliders capable of being taken out from a single wafer increases, and it is also suitable for the reduction in size of a magnetic disk drive. In a magnetic disk drive of a load/unload type, a slider sometimes strikes against the surface of a magnetic disk at the time of loading thereof from a ramp. Therefore, in a magnetic disk drive of a load/unload type, in order to ensure safety of recorded data, a non-recording area is usually provided outside an outermost radius track on a magnetic disk. Since the femto slider is small-sized, it is advantageous in that the width of the non-recording area can be decreased and the recording capacity of the magnetic disk can be increased thereby. In this case, a magnetic disk having a smaller diameter is more advantageous.
Since the longitudinal size of the femto slider is about 70% of that of the pico slider, there accrues an advantage such that the flying height compliance performance for disk curvature formed in the track circumference direction on a rotating magnetic disk surface is superior and a flying height of the slider becomes stable. When the femto slider and the pico slider are allowed to fly over the same disk and their amounts of change in flying height are compared with each other, the amount of change in flying height of the femto slider based on an ideal flying height over a magnetic disk, i.e., flying sensitivity, is about half of that of the pico slider.
In the case of the femto slider, the area of an air bearing surface (ABS) formed on its side opposed to the magnetic disk is about half of that of the pico slider. The femto slider has heretofore been used in a 2.5-inch type magnetic disk drive having a nominal magnetic disk diameter of 2.5 inches (1 inch=25.4 mm), but the application thereof to a smaller-size magnetic disk drive such as one having a nominal magnetic disk diameter of 1 inch or less is also very advantageous because of such advantages as the reduction in width of the non-recording area and in size.
In a small-sized magnetic disk drive having a small diameter of a spindle bearing and a small radius up to an innermost radius track, there sometimes occurs a case where, unless the rotational speed is increased, there is not obtained a sufficiently high flow velocity of an air current for forming an air bearing in the innermost radius track disposed on the innermost side. A solution to this problem is known wherein the rotational speed of a spindle motor is increased to increase the linear velocity of the innermost radius track. But this method is restricted by such problems as an increase in power consumption and the need of a high voltage for driving the spindle motor. Thus, for adopting the femto slider in a small-sized magnetic disk drive, it is necessary to solve various problems caused by a decrease in the ABS area of the slider and a decrease in the flow velocity of the air current.
In US 2003-0218832 describes an example in which a femto slider is applied to a 2.5-inch type magnetic disk drive and a suspension load is set at 29.4 mN (see paragraph [0096] and FIG. 8). On page 53 of Structure and Application of Hard Disk Drive, CQ Publishing Co., Ltd., published Jul. 1, 2003, there is a description to the effect that a femto slider is used at a spring load of 1 to 2 gf (9.8 mN to 19.6 mN).